JP3988828B2 - Dielectric constant measuring method and dielectric constant measuring apparatus - Google Patents

Description

  The present invention relates to a dielectric constant measuring method and a dielectric constant measuring apparatus by a reflection method in which a radio wave is irradiated from an antenna toward a measured object, a reflection coefficient thereof is measured, and a dielectric constant of the measured object is calculated. The present invention relates to a dielectric constant measuring method and a dielectric constant measuring apparatus that can measure the dielectric constant of snow without subjecting the snow to artificial work.

  In general, the snow quality and snow depth of snow cover change due to changes in the external environment, and the cross section of the snow has a layer structure, and the dielectric constant changes due to changes in the density inside the layer structure. Currently, there is data that measured the dielectric constant of snow in the microwave band, but there is no measurement data in other frequency bands, and naturally there is no measuring device that measures the dielectric constant. Therefore, the inventors measured the dielectric constant of snow at 1999 Aomori Airport by the transmission method, which is one of the common dielectric constant measurement methods.

  As shown in FIG. 8, in this device for measuring the dielectric constant of snow by the transmission method, a transmission board 52 capable of transmitting radio waves 51 is laid on the ground 50, and the radio waves 51 are transmitted below the transmission board 52 (underground). A transmitting horn antenna 53 that irradiates the surface of the transmission board 52 is provided. Above the transmission board 52 (ground), a receiving horn antenna 54 having a similar shape for receiving the radio wave 51 (transmitted wave) is supported by the support 56 and disposed opposite the transmitting horn antenna 53. . The receiving horn antenna 54 is connected to a network analyzer (not shown) that measures the transmission characteristics of the transmitted wave.

In such a configuration, when the radio wave 51 is irradiated toward the snow cover 55 on the transmission board 52, the radio wave 51 passes through the snow cover 55 and the transmission board 52 and is received by the reception horn antenna 54. The transmission characteristics of the received transmission are measured by a network analyzer (not shown), a transmission coefficient is calculated from the transmission characteristics, and the complex dielectric constant of the snow cover 55 is obtained.
Akira Togawa and two others, "Measurement of dielectric constant of snow in UHF band, Proceedings of the 2000 Annual Meeting of the Japanese Society of Snow and Ice, September 20, 2000, p.165

  Since it is configured in this way, due to fluctuations in weather, temperature, etc., the measurement equipment such as a network analyzer and a coaxial cable (not shown) has its electric characteristics fluctuated, resulting in measurement errors. Therefore, before measuring the dielectric constant of the snow cover 55, it is necessary to calibrate these measuring instruments. For that purpose, first, after removing the snow 55 accumulated on the transmission board 52, the radio wave 51 is irradiated with only the transmission board 52 (no snow), and the measuring instrument is calibrated from the transmission waves. Then, after performing the work of stacking the snow cover 55 on the transmission board 52 to form a flat snow cover surface as before, the transmission characteristics of the snow cover are measured, and the transmission coefficient obtained from the transmission characteristics is measured. It was necessary to calculate the dielectric constant from

  As described above, since the artificial work is performed on the snow cover 55 to be measured, the density inside the snow cover 55 is different from that of the snow cover 55 that has fallen naturally, and changes depending on the location. Therefore, the measurement result has a problem that the error of the imaginary part of the dielectric constant greatly changes with respect to the frequency.

  Furthermore, depending on the frequency band of the radio wave 51 used for measurement, the shape of the transmitting and receiving horn antennas 53 and 54 becomes large, so that the influence of wind pressure increases, and the measured value fluctuates due to antenna vibration and external waves. In addition, there is a problem that the support column 56 that supports the receiving antenna 54 must be made higher. Furthermore, when it was installed at the airport and this data was used to monitor the flight course during snowfall, there was a problem that it could not be installed due to the height restriction from the runway surface.

According to a first aspect of the present invention, there is provided a method for measuring a dielectric constant by a reflection method in which a measured object is irradiated with a radio wave and a dielectric constant of the measured object is calculated from the reflected wave. A measuring system having a measuring antenna comprising an antenna and a receiving antenna for measurement, and a coaxial cable connecting the measuring antenna to a coaxial switch, and having an electrical characteristic equal to the electrical characteristic of the measuring system and being coaxial Each with a transmission cable for calibration of the through connected to the switch, the object to be measured is snow,
During initial calibration after removing snow ,
(1) Switch the coaxial switch to the measurement antenna side, measure the initial calibration characteristics in the measurement system with a network analyzer, obtain the initial calibration coefficient of the measurement system from the initial calibration characteristics, save this,
(2) Next, the coaxial switch is switched to the calibration transmission cable side, the calibration characteristic is obtained by a network analyzer, the initial calibration coefficient of the calibration system is obtained from this calibration characteristic, and this is stored.
(3) The initial calibration coefficient of the calibration system is subtracted from the initial calibration coefficient of the measurement system, and this is stored as a transmission coefficient value between the transmitting and receiving antennas.
(4) The relative position and direction of the measurement transmitting antenna and the measurement receiving antenna are made constant, and the coupling coefficient between antennas is measured according to the procedures of (1) to (3) with the reflector removed. Subtract the vector from the transmission coefficient between the transmission and reception antennas, save this as the initial value of the calibration value at the time of measurement,
At the time of measuring the state where snow is placed on the reflector,
( 5 ) Switch the coaxial switch to the calibration transmission cable side, measure the calibration characteristics with a network analyzer, and obtain the calibration coefficient for measuring equipment calibration at the time of measurement from this calibration characteristics.
( 6 ) Next, the product of the calibration coefficient for calibration of the measuring instrument and the stored initial value is obtained, and this is transferred to the network analyzer as a true reflection coefficient for calibration of the measuring instrument at the time of measurement. To find its reflection coefficient,
( 7 ) The dielectric constant of the snow is calculated from the obtained reflection coefficient ,
(8) From the calculated dielectric constant of snow, based on the empirical formula derived in the VHF to microwave band, the dielectric constant in other frequency bands is calculated from the frequency band of the radio wave used for measurement by extrapolation. This is a method for measuring the dielectric constant.

The invention according to claim 2 irradiates radio waves to the measurement object, the dielectric constant measuring apparatus according to the reflection method of calculating the dielectric constant of the object to be measured from the reflected wave, the object to be measured is reflecting board for reflecting radio waves A measurement antenna comprising a measurement transmission antenna and a measurement reception antenna having the same electrical characteristics and shape, a coaxial cable connecting the measurement antenna to a coaxial switch, and a measurement antenna. A measurement system is configured and has electrical characteristics equal to the electrical characteristics of the measurement system. The through calibration transmission cable connected to the coaxial switch, and the network analyzer connected to the calibration transmission cable and measurement. A coaxial switch having means for switching between the system, the calibration transmission cable and the measurement system via the coaxial switch, and a calibration transmission cable and Network analyzer that measures the calibration characteristics from the stationary system, the reflection characteristics from the measurement system, and the coupling characteristics between the antennas, the function to calculate the calibration coefficient and the reflection coefficient from the reflection characteristics and the calibration characteristics, respectively, and the initial value of the measurement equipment calibration value a function of obtaining and a function of storing these values, the function of calculating the dielectric constant of the snow from the reflection coefficients of the measured snow, dielectric constant of the calculated snow, are derived in VHF~ microwave band A dielectric constant measuring apparatus having a personal computer having a function of converting a frequency band of radio waves used for measurement by an extrapolation method into another frequency band based on an empirical formula .

The invention according to claim 3 is the dielectric constant measuring apparatus according to claim 2, wherein the frequency band of the radio wave uses a C band.

In the inventions according to claims 1 and 2, it is not necessary to remove the snow cover on the reflecting plate at the time of calibration of the measuring device, and it does not take time. In particular, when measuring the dielectric constant of snow, it is not necessary to perform artificial work on the snow as in the past, so the density inside the snow can be obtained in a natural state, and the outside temperature and daily It is possible to accurately measure the dielectric constant for natural snow that fluctuates due to changes in snow.

In addition, measurement devices such as antennas for measurement and coaxial cables are installed outdoors, and there is no need to consider the expansion and contraction of coaxial cables due to changes in the ambient temperature even when measuring for long periods. Therefore, the electrical characteristics of the calibration system and the measurement system do not differ. In addition, the influence of the direct reception wave between the transmission for measurement and the reception antenna can be eliminated. Furthermore, there is no problem caused by reception of a reflected wave from the wall surface of the snow formed around the calibration system reflector in the first embodiment, and the measurement accuracy is improved accordingly. In addition, the apparatus itself is simplified, and there is an effect that it is not necessary to add any manual work to the snow cover even during calibration.

Further, the inventions according to claims 1 and 2 improve the reflection efficiency and also reduce the diffusion of reflected waves due to irregular reflection. In addition, the dielectric constant of the snow that naturally falls on the reflector can always be measured accurately in real time.

The invention according to claim 3 has the same effect as the inventions according to claim 1 and claim 2. Furthermore, since the measurement antenna can be measured using a frequency band that can reduce the size (for example, C band) and can be converted into a desired frequency band (for example, ILS glide path frequency), the shape of the antenna is large. There is no need to use an antenna or the like. Therefore, as in the prior art, it is possible to eliminate problems such as variations in measured values due to antenna vibration and external waves due to the influence of wind pressure, and the height of the measurement antenna. In addition, there is no need to remove snow on the reflector during calibration of the measuring instrument, and the dielectric constant can always be measured more accurately in real time.

In a method for measuring a dielectric constant by a reflection method in which a measured object is irradiated with radio waves and the dielectric constant of the measured object is calculated from the reflected wave, a measurement transmitting antenna and a measuring receiving antenna having the same electrical characteristics and shape are used. A measurement system having a measurement antenna and a coaxial cable connecting the measurement antenna to the coaxial switch, and an electrical characteristic equal to the electrical characteristic of the measurement system, Each with a calibration transmission cable, and the object to be measured is snow, and during initial calibration after removing snow ,
(1) Switch the coaxial switch to the measurement antenna side, measure the initial calibration characteristics in the measurement system with a network analyzer, obtain the initial calibration coefficient of the measurement system from the initial calibration characteristics, save this,
(2) Next, the coaxial switch is switched to the calibration transmission cable side, the calibration characteristic is obtained by a network analyzer, the initial calibration coefficient of the calibration system is obtained from this calibration characteristic, and this is stored.
(3) The initial calibration coefficient of the calibration system is subtracted from the initial calibration coefficient of the measurement system, and this is stored as a transmission coefficient value between the transmitting and receiving antennas.
(4) The relative position and direction of the measurement transmitting antenna and the measurement receiving antenna are made constant, and the coupling coefficient between antennas is measured according to the procedures of (1) to (3) with the reflector removed. Subtract the vector from the transmission coefficient between the transmission and reception antennas, save this as the initial value of the calibration value at the time of measurement,
At the time of measuring the state where snow is placed on the reflector,
( 5 ) Switch the coaxial switch to the calibration transmission cable side, measure the calibration characteristics with a network analyzer, and obtain the calibration coefficient for measuring equipment calibration at the time of measurement from this calibration characteristics.
( 6 ) Next, the product of the calibration coefficient for calibration of the measuring instrument and the stored initial value is obtained, and this is transferred to the network analyzer as a true reflection coefficient for calibration of the measuring instrument at the time of measurement. To find its reflection coefficient,
( 7 ) The dielectric constant of the snow is calculated from the obtained reflection coefficient ,
(8) From the calculated dielectric constant of snow, based on the empirical formula derived in the VHF to microwave band, the dielectric constant in other frequency bands is calculated from the frequency band of the radio wave used for measurement by extrapolation. I tried to do it.

  The first embodiment of the present invention constitutes two systems, a calibration system including a pair of calibration antennas for calibrating a measuring instrument such as a network analyzer and a coaxial cable, and a measurement system including a pair of measurement antennas. In addition, these two systems are configured so that the antenna, coaxial cable cable length, loss and antenna height, shape, etc. are all equal so that the electrical characteristics of both systems are the same, and the reflection characteristics of the object to be measured by the network analyzer 1 is measured, and the reflection coefficient is calculated from the reflection characteristics to calculate the dielectric constant ε of the object to be measured, which will be described below with reference to FIG.

  FIG. 1 shows a first embodiment of the present invention. Reference numerals 1 (1a, 1b) denote measurement antennas having the same electrical characteristics and shape, and from a signal source (not shown). Measurement transmitting antenna 1a for irradiating the object 3 to be measured 3 placed on the metal reflector 7 installed on the ground 6 and measurement for receiving the reflected wave 4 from the object 3 For this embodiment, a horn antenna is used.

  5 (5a, 5b) is a calibration antenna having a pair having the same electrical characteristics and shape, and the measurement antenna 1 has the same electrical characteristics and shape. The calibration antenna 5 (5a, 5b) is a calibration transmitting antenna 5a that irradiates a radio wave 2 toward a metal reflector 8 installed on the ground 6 and a calibration that receives a reflected wave from the reflector 8. And the receiving antenna 5b.

  In this embodiment, the measurement frequency band of the radio wave 2 is a C band, a horn antenna is used as a measurement and calibration antenna, and a device under test 3 for measuring a dielectric constant is provided on a reflector 7. It was assumed that the snowfall was piled up (hereinafter also referred to as snowfall 3). In this embodiment, the object to be measured 3 is measured by the snow cover 3, but is not limited to this, and other dielectric materials can be measured in the same manner.

  The reflection plates 7 and 8 are made of metal that reflects radio waves and are for increasing the reflection efficiency, and are installed on the ground 6 on both the calibration system side and the measurement system side. In the case of this embodiment, a heating device (not shown) is connected to the reflection plate 8 installed in the calibration system, and the reflection plate 8 is always heated during the snowy season. It is configured so that snow does not accumulate on the surface. On the reflection plate 7 of the measurement system, natural snow as the object to be measured 3 is formed.

  Both the measurement antenna 1 and the calibration antenna 5 are mounted so as to be movable in the horizontal direction at positions equidistant from the center line of the pole 11 spanned between the two supports 9 and 10. At that time, the measurement antenna 1 is attached above the DUT 3 and the installation angle between the measurement transmission antenna 1a and the measurement reception antenna 1b is such that the radio wave radiated from the measurement transmission antenna 1a is All are reflected by the device under test 3 and received by the measurement receiving antenna 1b so that the direct wave 4a is not received. A radio wave indicated by a broken line indicates a transmitted wave that passes through the DUT 3 and is reflected by the reflecting plate 7.

  Similarly, the calibration antenna 5 is mounted above the reflector 8, and the installation angle between the calibration transmission antenna 5 a and the calibration reception antenna 5 b is the same as that of the measurement antenna 1. The radio wave 2 radiated from is reflected by the reflecting plate 8 and received by the calibration receiving antenna 5b, so that the direct wave 4a is not received.

  In this embodiment, two support columns 9 and 10 are used. However, this is used as one support column, and the center portion of the pole 11 is fixed to the support column. The measurement antenna 1 and the calibration antenna 5 may be attached to each other, and the measurement system and the calibration system may be arranged on both sides around the support column.

  A coaxial switch 12 is connected to the network analyzer 15 and has means for switching between the measurement system and the calibration system. The measurement and calibration antennas are connected via the measurement system coaxial cable 13 and the calibration system coaxial cable 14. 1 and 5 are connected. The measurement system includes a measurement system coaxial cable 13 and a measurement antenna 1 and the calibration system includes a calibration system coaxial cable 14 and a calibration antenna 5 and the like.

  The network analyzer 15 measures the reflection characteristics of the reflected wave. The coaxial switch 12 switches between the measurement system and the calibration system, and the device under test 3 received by the measurement receiving antenna 1b and the calibration receiving antenna 5b, respectively. The reflection characteristics of the reflected wave from the reflector 8 are measured. Reference numeral 16 denotes a personal computer, and the reflection coefficient is calculated from the measurement results of the reflection characteristics in the measurement system and the calibration system measured by the network analyzer 15, and then the dielectric constant ε of the DUT 3 is calculated from the obtained reflection coefficient. Is done.

Next, a description will be given of a case where the dielectric constant ε of the snow that has actually fallen naturally on the reflector 7 as the object to be measured 3 (hereinafter referred to as snow 3) is obtained.
Here, snow falls naturally on the reflection plate 7 of the measurement system, and the snow cover 3 is formed, and the reflection plate 8 of the calibration system is always heated. Therefore, there is no snow cover 3 on the reflection plate 8. Suppose that it is in a state. Therefore, in order to obtain the dielectric constant ε of the snow cover 3 accumulated on the reflection plate 7 of the measurement system, the reflection characteristics of the snow cover 3 are measured using the above-described device, the reflection coefficient is obtained from the reflection characteristics, and this reflection The dielectric constant must be calculated from the coefficient.

  First, since the electrical characteristics of the measuring device fluctuate due to expansion and contraction of the network analyzer 15, the measurement system coaxial cable 13, and the calibration system coaxial cable 14 due to weather conditions and temperature changes, the measurement devices are calibrated. In this case, it is performed in a state where there is no snow on the reflection plate 8 in the calibration system. In the case of this embodiment, since the calibration reflector 8 is always heated, there is no snow on the surface. Therefore, when the coaxial switch 12 is switched to the calibration system and the radio wave 2 is irradiated from the calibration transmitting antenna 5a, the reflected wave from the reflecting plate 8 is received by the calibration receiving antenna 5b and the reflection characteristic of the reflected wave is received by the network analyzer 15. Measured. A reflection coefficient is obtained from the reflection characteristics measured at the time of calibration, and thereby the measurement equipment such as the network analyzer 15, the measurement system coaxial cable 13, and the calibration system coaxial cable 14 is calibrated.

  Next, the coaxial switch 12 is switched to the measurement system, the radio wave 2 is irradiated from the measurement transmission antenna 1a onto the snow cover 3 on the reflection plate 7, and the reflected wave is similarly received by the measurement reception antenna 1b. The reflection characteristic is measured by the network analyzer 15. In this way, the reflection coefficient during snow accumulation is similarly obtained from the measured reflection characteristics. The dielectric constant of the snow cover 3 is calculated from this reflection coefficient. As described above, the reflection characteristic is measured at the time of measurement, and the reflection coefficient is obtained from the reflection characteristic. At the time of calibration, the coaxial switch 12 is switched to the calibration antenna 5 to calibrate the measurement system drift due to the passage of time and the change of the outside air temperature each time. The reflection coefficient is obtained from this reflection characteristic, and the change in the dielectric constant of the snow cover 3 can be measured over the long term.

  Since the dielectric constant of the snow cover 3 calculated as described above is a result of measurement in the C band frequency band, the following empirical formula is measured and experimentally derived at a specific frequency in the VHF to microwave band. Based on the above, the dielectric constant converted to the frequency band of the glide path installed at the airport is calculated by extrapolation. Hereinafter, a conversion method for converting the snow complex permittivity measured at a specific frequency (VHF to microwave band) into a permittivity at an arbitrary frequency will be described.

  Assuming that the dispersion characteristics of snow containing moisture can be expressed in correspondence with the dispersion characteristics of water given by the Deby equation, the imaginary part ε "s (f) of the snow cover dielectric constant at the frequency f and the real part ε's of the snow cover dielectric constant For the increment Δε ′s (f) of (f), the following equations (A) and (B) are used, respectively.

Here, ε "s is the imaginary part of the snow permittivity, Δε's is the increment of the snow permittivity real part ε's due to the snow moisture, and ε's = ε'd + Δε's (where ε'd is the volume occupied by water) The real part of the dielectric constant when air is replaced with dry snow.) F ₀ is the dielectric relaxation frequency of pure water, f ₀ = 8.84 (GHz), and tan
δw is a dielectric loss tangent (loss factor) of pure water, and at a temperature of 0 ° C., the following equation (C) is obtained.

Here, the measurement value of the real part and the imaginary part of the complex dielectric constant at a frequency f _M, respectively _{ε's (f M), ε} " if s (f _M), the complex dielectric constant of the snow 3 at an arbitrary frequency f The imaginary part of is represented by the following equation (D) using equation (A).

  Next, the real part of the complex permittivity of the snow cover 3 is expressed by the following equation (E) using the equations (A), (B), and (C) from the above ε's = ε'd + Δε's.

  Here, the inventors assume that the empirical formula of Hallikainmenn et al. Reported in the frequency band of 3 to 37 (GHz) is also effective for the frequency band of 3 (GHz) or lower. The results of calculating the dielectric constant of the snow cover having a volume water content of 0 to 12 (%) and a density of 0.25 (g / cm 3) in the 0 to 5 (GHz) band are shown by solid lines in FIGS. With this data, assuming that the complex permittivity at f = 5 (GHz) is a known measured value, the result of newly calculating the complex permittivity for the frequency f <5 (GHz) from the equations (D) and (E) A marker plot was made. As is clear from this result, it was found that both agree well.

  Thus, since the dielectric constant of the snow cover 3 was obtained, when the network analyzer 15 was calibrated as in the past, the snow cover on the reflector 8 was removed to measure the reflection characteristics when the measuring device was calibrated. After obtaining the reflection coefficient from the reflection characteristics and obtaining the calibration value, it is necessary to make a flat snow surface again at the time of measurement. However, this work is not necessary. Therefore, it is possible to eliminate the fluctuation of the density inside the snow cover due to human work, and to obtain more accurate measurement data based on natural snow cover.

  However, in the first embodiment, since measurement devices that affect measurement data such as the measurement and calibration antennas 1 and 5 and the measurement system and calibration system coaxial cables 13 and 14 are installed outdoors, a long-term operation is required. In the case of measurement, the relative distance between the measurement and calibration antennas 1 and 5 and the reflectors 7 and 8 due to expansion / contraction of the measurement system and calibration system coaxial cables 13 and 14 due to a change in ambient environmental temperature, wind pressure vibration, etc. The electrical characteristics of the calibration system and the measurement system differ due to the fact that the general position fluctuates and the way the two antennas fluctuate.

  In addition, a snow wall is formed around the calibration reflector 8, and even if a highly directional antenna is used as the calibration antenna 5, the snow around the reflector 8 may be slightly fluctuated. The reflected wave from the wall surface is received. As described above, the reflected wave from the snow wall cannot be completely removed, which causes a measurement error. Furthermore, in the first embodiment, since a heating device is installed in the calibration reflector 8, there is a problem that the power consumption is increased and the cost is increased. When the heating device is not installed, it is not necessary to remove snow on the reflection plate 7 of the measurement system, but it is necessary to remove snow on the reflection plate 8 of the calibration system each time measurement is used. However, there are also problems such as taking time and effort.

  Therefore, in the second embodiment of the present invention, as shown in FIG. 4, instead of the calibration antenna 5 and the reflecting plate 8, a through coaxial cable (hereinafter referred to as a calibration transmission cable 20) is used in the calibration system. Hereinafter, it will be described in detail with reference to FIGS. In addition, the same thing as the said Example 1 uses the same code | symbol and the same name, and abbreviate | omits the description.

  FIG. 4 is a block diagram showing the second embodiment, FIG. 5 is an explanatory diagram of FIG. 4, FIG. 6 is a vector diagram, and FIG. 7 shows a geometric model of the reflection method. As in the first embodiment, the measurement antenna 1 includes a measurement transmission antenna 1a and a measurement reception antenna 1b, and a measurement-system coaxial cable 13 that connects the coaxial switch 12 and the measurement antenna 1. A measurement system is constituted by the measurement antenna 1 and the like.

  The calibration transmission cable 20 constituting the calibration system is the same as that of the measurement system in place of the calibration system coaxial cable 14 that connects the calibration antenna 5 and the reflector 8 and the calibration antenna 5 and the coaxial switch 12 in the first embodiment. It is formed of a straight through coaxial cable having electrical characteristics exactly equal to the electrical characteristics. In addition, only the reflecting plate 7 for measurement in Example 1 is used as a reflecting plate installed in order to improve reflection efficiency. Others are the same as in the first embodiment.

  In the second embodiment, as shown in FIG. 5, the coaxial switch 12 is connected to the network analyzer 15 by two coaxial transmission lines 21 and 22, and switches between the calibration transmission cable 20 and the measurement system. Means and is installed in the vicinity of the measurement antenna 1.

  Further, as shown in FIG. 5, the calibration transmission cable 20, the coaxial cable 23a for connecting the measurement transmission antenna 1a and the coaxial switch 12, and the coaxial for connecting the measurement reception antenna 1b and the coaxial switch 12 are connected. The cable 23b is preferably a cable of the same type, and the sum of the electrical lengths of the coaxial cable 23a and the coaxial cable 23b is equal to the electrical length of the calibration transmission cable 20 and the line length is preferably short.

Based on FIGS. 4 and 5, the case where the dielectric constant ε of the snow cover 3 that has actually fallen naturally as the device under test 3 will be described.
First, the outline of the second embodiment will be described as follows.
That is, in order to eliminate measurement errors due to fluctuations in the network analyzer 15 due to temperature changes, expansion / contraction of the coaxial cable portion, etc., first, the network analyzer calibration coefficient measured with the measurement antenna 1 when there is no snow 3 is used for calibration. The inter-antenna transmission coefficient is obtained by subtracting the network analyzer calibration coefficient obtained by switching to the transmission cable 20 side. Further, in the same procedure, the inter-antenna coupling coefficient is measured in the state in which the sky direction is directed without changing the relative position of the measuring transmitting antenna 1a and the measuring receiving antenna 1b, and is subtracted in vector from the inter-antenna transmission coefficient. To do. This basically means that the measurement device calibration value excluding the influence of the coupling between the antennas and the coaxial cable portion is measured, and this value is stored in the personal computer 16 as the initial value of the measurement device calibration value. The measurement device calibration value (initial value) is a unique value as long as the antenna characteristics of the measurement antenna 1 do not fluctuate.

  Next, in the snowy condition, measure the calibration value of the coaxial cable part and add it to the stored measuring device calibration value (initial value) to obtain a new measuring device calibration value (calibration value during snowfall). The measurement error due to the direct wave component from the measurement transmission antenna 1a to the measurement reception antenna 1b, the calibration value error due to the fluctuation of the network analyzer 15 due to the temperature change at the time of measurement, the expansion and contraction of the coaxial cable portion, and the like are eliminated. Unstable elements in the open space calibration system comprising the measurement antenna 1 can be eliminated. This will be described in more detail below.

First, a calibration method of the network analyzer 15 (a method for obtaining the initial value) in a state where there is no snow is described. This measurement is executed in a season without snow cover, and data to be acquired for long-term measurement is obtained.
First, the procedure for storing the initial value is obtained by the following procedure.
(1) Switch the converter 12 to the measurement antenna 1 side and perform response-through calibration. The calibration characteristic is measured by the network analyzer 15 from the reflected wave received by the measurement receiving antenna 1b, and the data of the calibration coefficient C _{# 1} (complex number) obtained from the calibration characteristic is stored in the personal computer 16.
(2) The coaxial switch 12 is switched to the calibration transmission cable 20 side to perform response through calibration. Similarly, the calibration characteristic is measured by the network analyzer 15, and the data of the calibration coefficient C _{# 2} (complex number) obtained from the calibration characteristic is stored in the personal computer 16.
(3) When the calibration coefficient C _{# 1} = | S _{# 1} | ^εj _{# 1} and the calibration coefficient C _{# 2} = | S _{# 2} | ^εj _{# 2} , the transmission antenna for measurement 1a and the reception antenna for measurement 1b The transmission coefficient seen from the connector end is
^{_{S 21 R = (C # 1}} / C # 2) = | S ♯1 | ε j♯1 / | S ♯2 | ε j♯2
= | S _{# 1} / S _{# 2} | ε ^(j _{# 1-} ^εj _{# 2} ⁾ = | S ^R ₂₁ | ε ^jφR ₂₁
It is represented by Therefore, the transmission coefficient S ^R ₂₁ can be calculated from the calibration coefficient C _{# 1} and the calibration coefficient C _{# 2,} but is corrected because it includes coupling between antennas.
(4) The procedure of (1) to (3) is executed in a state where the reflector 7 is not present with the relative position between the antennas fixed, for example, in a state where the two antenna openings are directed in the sky direction above. Then, the coupling coefficient S ^D ₂₁ between the antennas is measured and stored. As a result, as shown in FIG. ^6, the transmission coefficient ^S _{C 21} between the transmitting and receiving antennas that do not contain binding by subtracting from _{S R 21} and ^S _{D 21} vectorially ^{_{is, S C 21 = S R 21}} -S D 21 As required. This value is a unique value. Unless the characteristics of the measurement antenna 1 (coupling degree, gain, connector reflection characteristics) change, the transmission coefficient between the transmitting and receiving antennas is executed with the cable length changed due to temperature fluctuations. Even if the S ^C ₂₁ value is obtained, there is no change. Therefore, this is stored in the personal computer 16 as the initial value of the calibration value of the measuring device at the time of measurement.

Next, the measurement at the time of snow accumulation is executed according to the following procedure.
(5) The converter 12 is switched to the calibration transmission cable 20 side, and response loop calibration is performed. At this time, the calibration characteristic is measured by the network analyzer 15, and the calibration coefficient C _{# 2} ^M data obtained from the calibration characteristic is acquired.
(6) the calibration factor ^{_{C # 2 M = | S ♯2}} M | and _ε ^j φ2 ^M, obtaining the product of the transmission coefficients _{S 21} ^C that are stored.
^{_{C # 2 M S 21 C =}} | S ♯2 M | ε j φ2 M · | S 21 C | ε jφC 21 = S 21 M
This product S ₂₁ ^M is transferred to the network analyzer 15 as a new response calibration coefficient during snow cover.
(7) Next, the current measurement data is tracked. This value is the actual measured value when measured during snowfall.

In this way, the actual transmission coefficient at the time of snow accumulation is obtained, and the transmission dielectric constant ε of the snow accumulation 3 is obtained from this value by the reflection method.
In order to obtain the transmission dielectric constant ε of the snow cover 3, it is necessary to accurately measure the snow cover surface reflection coefficient Γ _TE when the TE wave is incident on the snow cover surface. Hereinafter, measurement of the snow cover reflection coefficient Γ _TE will be described.

  Here, as shown in FIG. 7, the antenna height H, the antenna directivity gain G, and the distance between the antennas of the transmitting antenna 1a and the receiving antenna 1b of the measuring antenna 1 are S. FIG. 7 shows a state where the calibration complete reflection surface is infinite and there is snow 3 (dielectric constant εr = εs−jεs) having a thickness d on the surface of the reflection plate 7.

The radio wave 2 irradiated with the transmission electric field Et from the measurement transmission antenna 1a is reflected by the surface of the snow 3 and received by the measurement reception antenna 1b. Here, the antenna axis Pa, P _b of the antennas 1a, 1b are assumed facing the reflection point P on the fully reflective surface. Also, it is assumed that the snow surface reflection coefficient for the transmitted spherical wave can be approximated by the reflection coefficient Γ _TE when the plane wave is incident (considered as plane wave propagation in the snow layer), and the coupling between the antennas 1a and 1b (direct wave) and The influence of multiple reflections between the antenna and the snow cover is negligible.

The received electric field strength _Erm when there is no snow is shown as the following formula (1).

k ₀ is a propagation constant in free space, and λ of the radio wave used for measurement is a wavelength. The measurement transmission and reception antenna gains are both G. The received electric field E _rs at the depth d of the snow cover 3 is expressed by the following equation (2) using Γ _TE .

Therefore, the received electric field E _rs at the depth d of the snow cover 3 with reference to the received electric field strength E _rm when there is no snow, that is, the measured transfer characteristic (for _obtaining the reflection coefficient) S ₂₁ is:

となる。

It becomes.

Here, in the formula (3), r / r _s is the propagation path length difference at the time of snow surface reflective metal surface reflection, represents the ratio of the propagation loss due to diffusion of transmission spherical wave, the antenna height H is snow It can be regarded as 1 if the distance is sufficiently longer than the depth d. G (θ _S ) / G (θ) is an antenna gain fluctuation ratio due to a difference in incident angle on the metal reflecting surface. These two terms, if not regarded as 1, the amplitude error of the gamma _TE. e ^{−j2k (2 kD (rs−r)} is a phase difference associated with the propagation path length. Since the measured S ₂₁ corrects these coefficients, it is a ^{highly accurate reflection for obtaining} the dielectric constant. A coefficient is obtained.

Since the dielectric constant of the snow cover 3 calculated as described above is a result of measurement in the C band frequency band, it was measured at a specific frequency in the VHF to microwave band from the calculated dielectric constant of the snow cover . Based on the experimental formula derived experimentally, the dielectric constant is calculated by converting to the frequency band of the glide path installed at the airport by extrapolation. Since this conversion method has already been described in the first embodiment, the description thereof is omitted.

It is a block diagram of the dielectric constant measuring apparatus which shows 1st Example of this invention. 1 is a frequency characteristic diagram of a real part of a relative permittivity according to a first embodiment of the present invention. FIG. 1 shows a first embodiment of the present invention and is a frequency characteristic diagram of an imaginary part of relative permittivity. FIG. It is a block diagram of the dielectric constant measuring apparatus which shows 2nd Example of this invention. FIG. 5 shows a second embodiment of the present invention and is an explanatory diagram of FIG. 4. FIG. 7 is a vector diagram showing a second embodiment of the present invention. The 2nd Example of this invention is shown and it is a geometric model figure of a reflection method. It shows a conventional example and is a configuration diagram of a dielectric constant measuring apparatus using a transmission method.

Explanation of symbols

1 antenna for measurement 2 radio wave 3 object to be measured (snow cover)
5 Calibration antenna 7 Reflector 12 Coaxial switch 15 Network analyzer 16 Personal computer
20 calibration transmission cable

Claims (3)

In the measurement method of the dielectric constant by the reflection method of irradiating the measurement object with radio waves and calculating the dielectric constant of the measurement object from the reflected wave,
A measurement system having a measurement antenna comprising a measurement transmission antenna and a measurement reception antenna having the same electrical characteristics and shape, and a coaxial cable connecting the measurement antenna to a coaxial switch, and electrical characteristics of the measurement system Each having a through-calibration transmission cable connected to the coaxial switch,
The object to be measured is snow,
At the time of initial calibration after removing the snow cover ,
(1) Switch the coaxial switch to the antenna side for measurement, measure the initial calibration characteristics in the measurement system with a network analyzer, determine the initial calibration coefficient of the measurement system from the initial calibration characteristics, and save this ,
(2) Next, the coaxial switch is switched to the calibration transmission cable side, the calibration characteristic is obtained by the network analyzer, the initial calibration coefficient of the calibration system is obtained from the calibration characteristic, and stored.
(3) Subtract the initial calibration coefficient of the calibration system from the initial calibration coefficient of the measurement system, and store this as a transmission coefficient value between the transmitting and receiving antennas;
(4) While keeping the relative position and direction of the measurement transmitting antenna and the measurement receiving antenna constant and excluding the reflector, the antennas are respectively connected according to the procedures of (1) to (3). Measure the coupling coefficient, subtract vector-wise from the transmission and reception antenna transmission coefficient value, save this as the initial value of the calibration value at the time of measurement,
At the time of measurement of the state where the snow is placed on the reflector,
( 5 ) Switch the coaxial switch to the calibration transmission cable side, measure the calibration characteristics with the network analyzer, and obtain a calibration coefficient for measuring equipment calibration at the time of measurement from the calibration characteristics,
( 6 ) Next, the product of the calibration coefficient for calibration of the measuring instrument and the stored initial value is obtained, and this is transferred to the network analyzer as a true reflection coefficient for calibration of the measuring instrument at the time of measurement. Trace the data, find its reflection coefficient,
( 7 ) The dielectric constant of the snow is calculated from the obtained reflection coefficient ,
(8) From the calculated dielectric constant of snow, based on the empirical formula derived in the VHF to microwave band, the dielectric constant in other frequency bands is calculated from the frequency band of the radio wave used for measurement by extrapolation. A method for measuring a dielectric constant. In a dielectric constant measuring device by a reflection method that irradiates a measured object with radio waves and calculates a dielectric constant of the measured object from the reflected wave,
The object to be measured is snow that has accumulated on a reflector that reflects radio waves,
A measurement antenna comprising a measurement transmission antenna and a measurement reception antenna having the same electrical characteristics and shape;
A measurement system comprising a coaxial cable connecting the measurement antenna to a coaxial switch and the measurement antenna is configured,
An electrical characteristic equal to the electrical characteristic of this measurement system, and a through transmission cable for calibration connected to the coaxial switch,
A coaxial switch connected to a network analyzer and having means for switching between the calibration transmission cable and the measurement system;
The calibration transmission cable and the measurement system are connected to the calibration transmission cable and the measurement system via the coaxial switch, the calibration characteristics from the calibration transmission cable and the measurement system, the reflection characteristics from the measurement system, and the coupling characteristics between the antennas. The network analyzer to be measured;
From the reflection characteristic, a function for calculating a calibration coefficient and a reflection coefficient from the calibration characteristic, a function for obtaining an initial value of the measurement instrument calibration value, a function for storing these values, and a reflection coefficient of the measured snow cover Based on the function to calculate the dielectric constant of this snow cover and the calculated dielectric constant of the snow cover, based on the empirical formula derived in the VHF to microwave band, the frequency band of the radio wave used for the measurement by the extrapolation method and other A personal computer with a function to convert to a frequency band ,
A dielectric constant measuring apparatus comprising: The dielectric constant measuring apparatus according to claim 2 , wherein a C band is used as a frequency band of the radio wave.

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